Door for microwave ovens



July 27, 1965 P. MULLER 3,197,600

DOOR FOR MICROWAVE OVENS Filed May 24. 1960 INVENTOR. m 374K641 BY/LLLQLL g Jvn'w United States Patent O 2 'Ciaiins. sci. ass mes This invention relates to doors for microwave ovens and similar apparatus. When used by nontechnical personnel, the construction of a microwave oven door should be such that it can be easily handled, prevents any radiation of the R-F energy, needs no further attendance, and in combination with the oven proper results in a unit of modern styling.

Earlier efforts to reach a tight contact between the door and oven made use of various types of contact fingers, sheet-metal strips, etc. To be most effective contact means of this type require an appreciable pressure to be applied and needed rather careful attendance to keep the contacts clean and free from fat. A solution like this is impossible when the oven is constantly used by laymen.

Other solutions not making use of electrically conducting contacts utilize a frame of conical profile at the oven and a door with an inner frame of corresponding profile. A door similar to this can be nicely styled, is easy to handle and needs no special care but some spots could always be detected where strong R-F leakage was present.

This invention relates to doors for microwave ovens without electrically conducting contacts between the door and oven.

This invention is characterized by a trough in the inner side of the door forming a continuation of the R-F room thereby adding at least a quarter-wavelength to the depth of R-F room.

A further object of the present invention is to provide the door with a border about a quarter-wavelength wide being in closest possible contact with the oven and the resulting air-gap having a length much greater than a quarter-wavelength.

For a better understanding of the invention, reference should now be made to the following detailed description which is to be read with the accompanying drawing showing a cross-section of the portion of interest of an oven with the door closed.

Referring now to the drawing, R-F room 1, preferably of rectangular cross-section, is bounded by metal walls 2. Door 4, which is pivoted on axis 3, is of a double-wall construction. The inner wall 5 of the door has the configuration of a trough. The length and width of the trough exactly correspond to the cross-section of the RF room and the trough-depth is at least a quarter of the free-space wavelength of the R-F generator used (gr/4). Gap 6 between the oven proper and the door border is less than one millimeter in depth. Both the oven and the door are finished in porcelain-enamel or lacquer thus prohibiting any electrical contact.

The trough affects a minimum distance of about a quarter-wavelength of the current plane from said gap. The gap itself is preferably placed along a voltage-plane. The R-F room can be exited in various modes, i.e., many wavelengths are present simultaneously, some of which may have a wavelength greater than the free-space wavelength of the R-F generator used. Taking into account the longer wavelengths would result in a rather bulky form of door. Tests showed that a trough depth of approximately a quarter of the free-space wavelength generated by the R-F generator is sufficient. Inner trough corners are rounded to facilitate cleaning.

The door-border directly opposite the oven having a small gap 6 between both is approximately a quarterwavelength wide, with the gap 6 extending for a length of some multiple of a quarter-wavelength. In this way favorable match of the free-space to the voltage maximum within the gap is accomplished.

Tests have shown a door built according to the above rules to avoid practically any R-F leakage. Means disclosed herewith allow production of a door achieving the goals mentioned before.

What I claim is:

1. In a microwave oven, in combination, an oven enclosure having surrounding walls and a front opening, said opening being defined by said surrounding walls and surrounded by a flanged rim of said walls extending at least partly in the plane of said opening; means for feeding microwave energy of a predetermined frequency into the interior of said oven enclosure; and an oven door movable into a position covering said opening of said oven enclosure, said door having marginal portions facing, when said door is in said position, said flanged rim of said walls and being spaced therefrom a small distance so as to form therewith a narrow gap, said door being formed with a recess extending outwardly from the plane of said marginal portions and facing the entire crosssectional area of the interior of said oven enclosure, the depth of said recess being substantially equal to A of the free-space wavelength of said microwave energy, the contour and cross-sectional area of said recess being substantially equal to that of said opening of said oven enclosure, said recess forming a direct extension of the interior of said enclosure, and the width of said marginal portions being substantially equal to A of the free-space wavelength of said microwave energy whereby leakage of microwave energy through said gap between door and oven enclosure is avoided.

2. An arrangement as claimed in claim 1, wherein said wall portions have extensions extending beyond the outer end of said flanged rim, and wherein said oven door has a rim portion in continuation of said marginal portions thereof, said rim portion facing said extension of said wall portions and being spaced therefrom by a gap having a width which is a multiple of that of said narrow gap between said marginal portions of said door and said flanged rim of said oven enclosure.

References Cited by the Examiner UNITED STATES PATENTS 2,500,676 3/50 Hall et al 2l9-10.55 2,622,187 12/52 Welch 2l910.55 2,831,952 4/58 Warner 2l910.55 2,888,542 5/59 Mork 21910.55 2,958,754 11/60 Hahn 1 .19-10.55

FOREIGN PATENTS 643,605 9/50 Great Britain.

RICHARD M. WOOD, Primary Examiner.

MAX L. LEVY, Examiner. 

1. IN A MICROWAVE OVEN, IN COMBINATION, AN OVEN ENCLOSURE HAVING SURROUNDING WALLS AND A FRONT OPENING, SAID OPENING BEING DEFINED BY SAID SURROUNDING WALLS AND SURROUNDED BY A FLANGED RIM OF SAID WALLS EXTENDING AT LEAST PARTLY IN THE PLANE OF SAID OPENING; MEANS FOR FEEDING MICROWAVE ENERGY OF A PREDETERMINED FREQUENCY INTO THE INTERIOR OF SAID OVEN ENCLOSURE; AND AN OVEN DOOR MOVABLE INTO A POSITION COVERING SAID OPENING OF SAID OVEN ENCLOSURE, SAID DOOR HAVING MARGINAL PORTIONS FACING, WHEN SAID DOOR IS IN SAID POSITION, SAID FLANGED RIM OF SAID WALLS AND BEING SPACED THEREFROM A SMALL DISTANNCE SO AS TO FORM THEREWITH A NARROW GAP, SAID DOOR BEING FORMED WITH A RECESS EXTENDING OUTWARDLY FROM THE PLANE OF SAID MARGINAL PORTIONS AND FACING THE ENTIRE CROSSSECTIONAL AREA OF THE INTERIOR OF SAID OVEN ENCLOSURE, THE 